1. Field of the Invention
The invention relates to the field of power semiconductor electronics.
It is based on a power semiconductor module according to the preamble of the first claim.
2. Discussion of Background
Such a power semiconductor module has already been described in German Offenlegungsschrift 39 37 045 A1.
A power semiconductor module generally comprises a plurality of semiconductor components, which can be combined to form a logical functional unit. Examples are rectifiers, individual switches having a reverse-connected parallel diode, or phase modules. Modules differ from the disk-type thyristors which are customary nowadays in the area of high power semiconductors essentially by the fact that the cooling and the power connections are electrically insulated from one another.
Such modules (thyristor, transistor, IGBT, MOSFET and diode modules) are widespread nowadays in the power range up to 1200 V and a few hundred A and are used primarily in industrial drives. Modules for high currents generally comprise a number of individual modules, which are connected in parallel in the module, or a plurality of modules are connected in parallel in the same way.
At present, there are upper limits to the performance of the modules in respect of current-carrying capacity and maximum blocking voltage as a result of the following problems:
The parasitic inductance of the internal structure of a module does not permit an arbitrary number of components to be connected in parallel. Turn-on and turn-off operations would lead to impermissible oscillations. In addition, the area of the individual components connected in parallel cannot be increased arbitrarily, for reasons of production costs and reliability. PA0 As the base area of the module increases, the reliability problems are exacerbated, especially in respect of the resistance, to be required, to temperature change, since the mechanical loading becomes larger and larger as the physical size increases and as a result of the different thermal expansion coefficients of the materials used. PA0 The creepage paths which can be achieved with a conventional module are generally too small for the insulation strength required for components which have a high blocking strength. PA0 The thermal resistance of a conventional module is relatively high compared with a structure having disk-type thyristors. The reason for this is the isolation of the thermal contact and the electrical contact, which necessitates the use of materials having low thermal conductivity compared with metals and enables only one of the main connections of the component to be cooled. Both main electrodes can be cooled in a disk-type thyristor. PA0 A module is screwed to a cold plate or a heat sink by means of screws (typically at all four corners). Reliable contact, which conducts heat well, can thus become problematic in the centre of the base area for a module having a very large area and can change during operation over time. PA0 In the case of a module, the main connections are arranged alongside one another on the top of the module. It is thus predetermined that a current loop, and hence an inductance, will be produced for the DC voltage connection.
In German Offenlegungsschrift 39 37 045, by R. Bayerer et al. and mentioned in the introduction, an attempt is therefore made to reduce the stray inductance and to specify a geometry which is suitable for a larger number of power transistors. For this purpose, the three main connection lines comprise wide strips, which are arranged at a small spacing from one another and form a connection stripline on account of their geometric arrangement. The lines which are routed vertically to the module base require the connection technique to be relatively complicated and make it more difficult to achieve adequate electrical insulation between one another, in particular if the inductance is to be low.
On the other hand, in German Offelegungsschrift 41 03 486 A1 by H. J. Krokiszinksi et al., an attempt is made to improve the dissipation of heat by cooling a module from both sides. However, the disadvantage of doing this is that the cooling medium flushes round the DC voltage connections as well and consequently has to be electrically insulating (for example deionized water). In addition, the DC voltage connections also form a conductor loop.